So I noticed an interesting problem:
# mknod foo c 4095 1048575
# ls -l foo
crw-r--r-- 1 root wheel 0, 0 Jan 17 05:25 foo
#
This is due to the special case for VNOVAL in ufs_mknod().
Technically, VNOVAL in any vattr field means `no value', so changing
this is really not correct.
What I wonder is why VOP_MKNOD() uses a vattr at all?! This seems
pretty bogus.